FFmpeg 9.1's new AAC encoder

FFmpeg 9.1 features a completely rewritten AAC encoder that outperforms competing encoders like qaac and fdk-aac across multiple quality metrics, according to benchmarks using Google's Zimtohrli and ViSQOL tools. The new encoder implements advanced coding tools (PNS, TNS, I/S, and M/S) within a rate-distortion optimization loop and uses perceptual masking to prioritize audible frequency bands. The encoder is optimized for CBR mode and 48kHz audio, and is now available in FFmpeg's main branch.